OBOR is a personal project of Xi's, who spoke of the importance of "harmonious co-existence" with other countries during the opening ceremony.

But that harmony was somewhat spoiled by North Korea's missile launch from a base near the Chinese border hours before Xi started speaking.

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Insult to Beijing

While analysts were careful of reading too much into the political timing of the missile launch -- pointing to technical considerations and favorable weather conditions -- they were clear the move would not be well received in Beijing.

"China will be greatly displeased," said Tong Zhao, an analyst with the Carnegie-Tsinghua Center for Global Policy.

He pointed to worsening relations between Beijing and Pyongyang as the US has increased pressure on China to act to rein in North Korea's nuclear program.

This month, North Korean state media warned China was crossing a "red line" in relations between the two countries as Beijing danced "to the tune of the US."

Zhao said that while Pyongyang may not have timed the launch to insult China, that it went ahead with it regardless showed they were unconcerned by potentially angering Beijing.

North Korea said the missile test was in response to the nuclear dangers and threats posed by the US and its followers.

"We will conduct ICBM tests anytime and anywhere in accordance with the decisions made by our central leadership," North Korea's ambassador to China Ji Jae Ryong said at an impromptu press conference at the country's embassy in Beijing Monday.

Ji's comments came as President Xi was due to speak himself at the close of the Belt and Road Forum.

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Also likely to be displeased was Russian President Vladimir Putin, who spoke at the forum shortly after Xi Jinping. According to a US official, Sunday's missile landed 60 miles (95 kilometers) south of Russia's Vladivostok region, home to the Russian Pacific Fleet.

It's unclear why North Korea would fire a missile so close to Russia. Euan Graham, an expert on North Korea at Australia's Lowy Institute, said it seemed to be a self defeating move by North Korean leader Kim Jong Un.

"Russia has until now shown no signs of wanting to get on board with tougher sanctions," Graham said.

In a statement, White House spokesman Sean Spicer said the move should "serve as a call for all nations to implement far stronger sanctions against North Korea."

Kremlin spokesman Dmitry Peskov said Sunday that Putin was concerned by the launch and the "escalation of tensions" in the region, according to state news agency TASS.

Missile advance

North Korea has conducted seven previous launches since the beginning of the year, though the most recent -- on April 29 -- was a failure, according to South Korean and US officials.

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Pyongyang has been rapidly advancing its missile program, with a stated goal of achieving a functioning intercontinental ballistic missile (ICBM) that could threaten the US mainland.

While Sunday's missile was far from that, Tsinghua's Zhao said it appeared to use a lofted trajectory indicating a potential range greater than previously tested weapons.

"North Korea wants to attain a credible regional nuclear capability with which it can hold regional targets under nuclear threat," he said.

He doubted whether Pyongyang would ever be able to build a functioning ICBM "because the US is putting real pressure on not only North Korea but all other countries."

But he warned that "with a regional nuclear deterrence, they might feel they are secure enough and do not really need a direct nuclear deterrence against the homeland of the US."

Graham said details about Sunday's missile "point to a new threshold of capability potentially crossed," adding that engineers "may well be able to draw warhead re-entry data from that which is applicable to their ICBM ambitions."

'Very anxious'

China is North Korea's chief ally and is seen by many as the main means for applying greater pressure on Pyongyang regarding its weapons programs.

Chinese media have become increasingly critical of North Korea in recent months, with state-sanctioned tabloid Global Times even questioning the relevance of the friendship treaty between the two countries.